Methods for blocking light using glass can be roughly divided into two groups, i.e., interference methods and absorption methods.
In the interference methods, a multilayer film is deposited on glass that does not absorb UV or visible light. By utilizing the light interference ability of the multilayer film, light in a certain wavelength range can be blocked.
The interference-type light blocking method is dependent on incidental angle. Therefore, light in a certain wavelength range that enters the glass perpendicularly can be blocked, but light that is incident from other angles cannot be blocked. Furthermore, a sharp blocking effect is difficult to obtain by the interference-type light blocking method due to its wide gradient wavelength range (Δλ), as defined by JIS B 7113.
In the absorption-type light blocking method, light having a wavelength in a certain range is blocked by using glass that contains light-absorbing ions, metal colloids, semiconductor fine particles and the like. In particular, semiconductor fine particles have excellent absorption ability.
Examples of known semiconductor fine particles include II-VI compound semiconductors, such as crystals of CdS, CdSe, CdSSe and like cadmium compounds. However, because cadmium compounds are toxic, they may impair the operator's health during batch mixing, transporting, melting and other steps. Furthermore, this method requires treating cadmium compounds contained in wastewater and waste material, which are generated during cutting, grinding, polishing and like glass-processing steps. Although some of the glass that contains the above-mentioned cadmium compounds has a wavelength of not less than 450 nm at a transmittance of 50%, it has a wide gradient wavelength range (Δλ), and therefore it is difficult to obtain a sharp blocking effect just as in the interference-type light blocking method.
A light-blocking technique by which light in a specific wavelength range can be absorbed by replacing the cadmium compound with Zn fine particles is disclosed in, for example, Patent Document 1. However, the light-blocking technique disclosed in Patent Document 1 still has a wide gradient wavelength range (Δλ), and therefore it is difficult to obtain a sharp blocking effect.
Ultraviolet-ray blocking glass and colored glass using copper (I) halide fine particles as group I-VII semiconductors, as semiconductor fine particles, are also known (Patent Documents 2 to 8).
Examples of copper (I) halide fine particles include fine particles of CuCl, CuBr, CuI and like compounds, and mixtures thereof. These copper (I) halide fine particles are not toxic and are easy to handle. The ultraviolet-ray blocking glass and colored glass containing such fine particles exhibit a narrow gradient wavelength range (Δλ) and achieve a sharp blocking effect.
However, when a high transmittance of visible light is desired in the glass that contains copper (I) halide fine particles described above (for example, when an average transmittance of not less than 85% at a wavelength in the range of 450 nm to 600 nm is desired from light having a wavelength in the range of 300 nm to 600 nm incident on a 1-mm-thick glass plate), since a transmittance of 50% is obtained at a maximum wavelength of 430 nm, even after adjusting the compositions and contents of the fine particles therein, longer-wavelength light, i.e., 430 nm to 450 nm, cannot be satisfactorily blocked. Therefore, the development of a light-blocking technique by which sharp blocking can be attained for wavelengths at around 450 nm is desired.                Patent Document 1: Japanese Unexamined Patent Publication No. 2005-206434        Patent Document 2: Japanese Unexamined Patent Publication No. 1992-018501        Patent Document 3: Japanese Unexamined Patent Publication No. 1992-275942        Patent Document 4: Japanese Unexamined Patent Publication No. 1993-105865        Patent Document 5: Japanese Unexamined Patent Publication No. 1993-201746        Patent Document 6: Japanese Unexamined Patent Publication No. 1994-024794        Patent Document 7: Japanese Unexamined Patent Publication No. 1995-048140        Patent Document 8: Japanese Unexamined Patent Publication No. 1996-337433        